1. Field of the Invention
The present invention relates to the field of water alert systems. More particularly, the present invention relates to a water activated power supply for signaling a control device of the detected presence of a body of water, and for triggering a bistate device upon the detection of a body of water.
2. Background
Water alert devices including a power source and a water activated switching circuit for triggering a bistate device, e.g. a horn, or a transmitter, are well known in the prior art. For example, see, U.S. Pat. Nos. 3,810,146; 4,079,364; 4,714,914; 4,777,478; 5,025,247; and 5,710,989. Typically, the power source is a battery, and the water activated switching circuit includes a transistor switch, a voltage divider, and a water activated switch in the form of a pair of electrodes. The horn or transmitter is electrically coupled between a positive terminal of a battery and a collector terminal of the transistor switch; the electrodes and the voltage divider are coupled in series between the positive terminal of the battery and a negative terminal of the battery; a base terminal of the transistor switch is electrically coupled to the voltage divider; and an emitter terminal of the transistor switch is electrically coupled to the negative terminal of the battery. The battery and the base terminal of the transistor switch are electrically uncoupled in the absence of both electrodes being simultaneously immersed in a body of water. Consequently, the transistor switch is in a cutoff mode of operation due to the lack of current to the base terminal of the transistor switch, and the transistor switch does not draw current from the battery. As a result, the horn or transmitter serially connected with the transistor switch is in a deactivated state of operation. The battery and the base terminal of the transistor switch are electrically coupled when the electrodes are simultaneously immersed in a body of water. Consequently, the transistor switch transitions to a saturation mode of operation due to the supply of current to the base terminal of the transistor switch, and current is drawn from the battery by the transistor switch to activate the horn or transmitter.
One problem associated with the utilization of a water activated switching circuit is that the magnitude of current supplied to the base terminal necessary to transition and maintain the transistor switch in a saturation mode of operation during the simultaneous immersion of both electrodes in a body of water can be relatively significant. Consequently, the usable life of the battery can be significantly reduced. Another problem with the utilization of a water activated switching circuit is the magnitude of the current drawn by the load placed on the battery due to the horn or transmitter during the simultaneous immersion of both electrodes in a body of water. This load can also significantly reduce the usable life of the battery. What is therefore needed is a water activated means for drawing a negligible amount of electrical power from a power source. What is also needed is a water activated means for isolating the power source from an external load device electrically coupled to the water activated means, e.g. a horn or a transmitter.